Transplantable lines of dimethylbenz(a)anthracene (DMBA)-induced fibrosarcomas exhibit cross-reactivity in the tumor immunity induced in histocompatible chickens with respect to serum antibody, delayed hypersensitivity (DTH), and transplant rejection. Both humoral and cellular immunity also exhibit cross-reactivity with embryo fibroblasts from the same chicken strain. Cross-reactivity also extends to transplantable tumors derived from methylcholanthrene and benzo(a)pyrene-induced fibrosarcomas. When SC chickens are injected with DMBA after they have been immunized with one tumor line and exhibit DTH and tumor rejection to that line at the age of 12 weeks, they develop a significantly lower incidence of primary fibrosarcomas than do control chickens during the following 5 months. During the initial 2 weeks after tumor transplantation, a transient stage of tumor immunity occurs that disappears when tumors grow progressively during the third week. Injection of low doses of cyclophosphamide can, under certain conditions, prevent progressive tumor growth, while an intravenous injection of irradiated tumor cells can cause progressive growth of a subsequent low-dose tumor challenge. Preliminary results of studies on organ-specific metastases in this tumor system suggest the presence of organ-specific receptors on the tumor cells that can be blocked by monoclonal antibody. (LB)